title: Membrane damage and viability loss of Escherichia coli K-12 and Salmonella enteritidis in liquid egg by thermal death time disk treatment.
abstract: Bacterial injury, including leakage of intracellular substance and viability loss, of Escherichia coli K-12 (ATCC 23716) and Salmonella Enteritidis (ATCC 13076) inoculated in liquid egg white and liquid whole egg was determined by thermal death time disk. E. coli K-12 and Salmonella Enteritidis were inoculated in liquid egg white and liquid whole egg to a final count of 7.8 log CFU/ml and were thermally treated with thermal death time disks at room temperature (23"C), 54, 56, 58, and 60 degrees C from 0 to 240 s. Sublethal injury, leakage of intracellular substances, and viability loss of E. coli K-12 and Salmonella Enteritidis was investigated by plating 0.1 ml on selective trypticase soy agar containing 3% NaCl, 5% NaCl, sorbitol MacConky agar, and xylose lysine sodium tetradecylsulfate and nonselective trypticase soy agar. No significant (P > 0.05) differences on percent injury or viability loss for E. coli K-12 and Salmonella populations were determined in all samples treated at 23 degrees C. Sublethal injury occurred in E. coli and Salmonella populations at 54 degrees C or above for 120 s. Viability losses for both bacteria averaged 5 log at 54 degrees C or above for 180 s, and the surviving populations were below detection (<10 CFU/ml). Thermal treatment at 40 degrees C and above led to membrane damage, leakage, and accumulation of intracellular ATP from 2 to 2.5 log fg/ml and UV-absorbing substances of 0.1 to 0.39 in the treated samples. These results indicate similar thermal injury/damage on both E. coli and Salmonella membranes as determined by the amount of inactivation, viability loss, and leakage of intracellular substances of bacteria.
authors.affiliation: Food Safety Intervention Technologies Research Unit, Eastern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038, USA. dike.ukuku@ars.usda.gov
authors.forename: Dike O
authors.initials: DO
authors.lastname: Ukuku
authors.forename: Tony
authors.initials: T
authors.lastname: Jin
authors.forename: Howard
authors.initials: H
authors.lastname: Zhang
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000473:pathology; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D004305:Dose-Response Relationship, Drug; D004531:Eggs / Q000382:microbiology*; D048168:Escherichia coli K12 / Q000254:growth & development*; D005506:Food Contamination / Q000517:prevention & control; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods; D006358:Hot Temperature; D006801:Humans; D012477:Salmonella enteritidis / Q000254:growth & development*; D012965:Sodium Chloride / Q000494:pharmacology; D013997:Time Factors
chemical_list: D012965:Sodium Chloride